Power meter arrangement

ABSTRACT

An electric power meter arrangement, includes a metrology unit configured to be coupled to a power line and to determine power consumption and provide measurement data representing the power consumption. A programmable control unit including a memory is configured to store software configured to run on the control unit. A security unit is configured to store at least one key and to validate that software stored in the memory of the programmable control unit is authorized.

TECHNICAL FIELD

Embodiments of the present invention relate to an electric power meterarrangement, for example, a smart electric power meter arrangement.

BACKGROUND

An electric power meter is adapted to measure the power consumption ofelectric loads connected to a power supply line. The power meter iscoupled to the supply line and measures the voltage at the supply lineand the current flowing through the supply line in order to determinethe power consumption.

A conventional electromechanical power meter includes a non-electronicdisplay that displays the power that has been consumed since the powermeter has been installed. An employee of the utility company regularly(usually a few times each year) evaluates the meter reading in order tocalculate the power consumption since the last evaluation and in orderto bill the customer accordingly.

A smart electric power meter is an electronic device that is coupled tothe power line and that is adapted to measure the power consumption andto store a measurement value representing the power consumption in amemory device. The memory can be read out on-site. Alternatively, thesmart meter may have an interface which connects the smart meter to acommunication network. Via the network the utility company can read thememory so that there is no need to have an employee on-site. The networkcan be any suitable network, like a wireless network, a telephonenetwork, or a power line.

Power consumption data, especially when they are transmitted to theutility company, are sensitive data, because they allow conclusions tobe drawn based on the consumer's habits and could, therefore, beabusively used for surveillance purposes by unauthorized third partiesthat may “eavesdrop” on the network. In addition, power consumption datamay be tampered with by the consumer in order to reduce electricitybills.

Some smart power meters include a switching arrangement (circuitbreaker) which can be remotely operated by the utility company in orderto interrupt the power supply when, for example, the customer does notpay the bill or is consuming an excess of power. It goes without sayingthat unauthorized operation of the circuit breaker may have severeconsequences for the consumer, but also on the stability of the grid.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a secure andtamper-proof meter.

In a first aspect an electric power meter arrangement, including ametrology unit is configured to be coupled to a power line in order todetermine power consumption and to provide measurement data representingthe power consumption. A programmable control unit including a memory isconfigured to store software configured to run on the control unit. Asecurity unit is configured to store at least one key and to validatethat software stored in the memory of the programmable control unit isauthorized.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples will now be explained with reference to the drawings. Thedrawings serve to illustrate the basic principles, so that only aspectsnecessary for understanding the basic principles are illustrated. Thedrawings are not to scale. In the drawings the same reference charactersdenote like features.

FIG. 1 illustrates a block diagram of a power meter arrangementaccording to a first embodiment, which includes a metrology unit, acontrol unit and a security unit;

FIG. 2 illustrates a block diagram of a power meter arrangementaccording to a second embodiment;

FIG. 3 illustrates one embodiment of a software authentication methodwhich can be performed by the security unit;

FIG. 4 illustrates an embodiment of an electric power meter arrangementwhich includes a switching circuit;

FIG. 5 illustrates an embodiment of an electric power meter arrangementin which the control circuit includes a communication interface forcommunication with a utility company;

FIG. 6 illustrates one embodiment of a power meter authentication methodperformed by the utility company and the security unit; and

FIG. 7 illustrates one embodiment of a utility authentication methodperformed by the utility company and the security unit.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a block diagram which illustrates a first embodiment of anelectric power meter arrangement, in particular, a smart power meterarrangement. The power meter arrangement includes a metrology unit 11which is configured to be coupled to a power line 100 and to determine apower consumption or, more precisely, an electrical energy consumption.The metrology unit 11 measures the electrical energy transferred via thepower line 100. This can be electrical energy transferred from asupplier (not shown), like a utility company, to a consumer or, moreprecisely, to electrical loads 51 (illustrated in dashed lines)connected to the power line 100 and operated by the user. However, thiscan also be energy transferred in an opposite direction from theconsumer to the supplier when, e.g., the consumer operates currentgenerating means, like solar panels.

The metrology unit 11 includes, for example, a sensing device 12 coupledto the power line 11 and configured to provide a measurement signal S12to an evaluation unit 13. The measurement signal S12 represents at leastthe current flowing through the power line 11, but may also include twosub-signals from which one represents the current flowing through thepower line 100, and one represents the voltage available at the powerline 100. The evaluation unit 13 is configured to calculate the powerconsumption from the current signal or from the current and the voltagesignal. According to the first alternative, the evaluation unit 13calculates the effective current (rms current) from the measured currentand calculates the power consumption based on the effective current andthe known (and usually only slightly varying) rms value of the voltageat the power line 100. According to the second alternative, theevaluation and storage unit 13 takes into account both the measuredcurrent value and the measured voltage value for calculating the powerconsumption.

The evaluation unit 13 is further configured to meter the evaluatedpower consumption in order to provide measurement data representing theaccumulated power consumption, which is the electrical energytransferred via the power line 100. The measurement data represent theenergy consumed since a given time in the past. For example, this timecan be the time at which the power meter has been installed, or the timeat which the measurement data have been read out from the metrology unit11 for the last time.

Optionally, the metrology unit 11 is configured to store severalmeasurement data (power meter readings), with each of these measurementdata representing the accumulated power consumption (energy consumption)at another time in the past. These measurement data provide a powerconsumption history which not only allows the determination of theabsolute energy consumption, but also allows the evaluation offluctuations in the power consumption. Storing a history of power meterreadings provides additional information, like the information at whichtimes the power consumption was relatively high or relatively low.

The metrology unit 11 with the sensing device 12 and the evaluation unit13 can be a conventional smart power meter metrology unit. Suchmetrology units are commonly known, so that no further explanations arerequired in this regard.

In FIG. 1 only one power line 100 is illustrated. However, the powermeter arrangement can be connected to more than one power line, likethree power lines in a three-phase power system. In this case the powermeter arrangement includes three sensing devices 12 which provide theirsensing signals to the evaluation unit 13.

The power meter arrangement further includes a control unit 20. Thecontrol unit 20 is configured to communicate with the metrology unit 11such that the control unit 20 may receive data, like measurement data,from the evaluation unit 13 and/or that the control unit 20 may providedata, like data for resetting the metrology unit 11 after themeasurement data have been retrieved, to the metrology unit 11. Acommunication link between the control circuit 20 and the metrology unit11 can be implemented in a conventional way with a direct link (asillustrated) between these two units 11, 20, or with a bus (notillustrated) which could also be used for data transmission to otherunits within the power meter arrangement.

The control circuit 20 includes a programmable device 21 with a memory22, in particular, a non-volatile memory, in which a software programcan be stored. The programmable device 21 can be implemented with amicrocontroller. According to one embodiment, the memory 22 is not onlyconfigured to store software, but is also configured to storemeasurement data retrieved from the metrology unit 11.

Optionally input/output means, like a display 23 and/or a keypad 24, areconnected to the programmable device 21 in the control unit 20. Theinput/output means allow a user to retrieve information from the controlunit 20, like measurement data stored in the programmable device 21 orevaluation data retrieved by the control unit 20 from the evaluationunit 13. Further, the display may be used to display tariff informationor service information, like a meter serial number, etc.

The measurement data displayed by the control unit 20 may, for example,be read by a person authorized by the utility company and may form thebasis for charging the consumer. It is, therefore, of utmost relevancethat measurement data which are displayed by the control unit 20 orwhich are transmitted to the utility company by other means are correct.The data retrieved from the evaluation unit 13 and displayed by thecontrol unit 20 or forwarded to the utility company are processed by theprocessing device 21 governed by the software stored in the memory 22.Assume that a third party with fraudulent intentions replaces thissoftware or firmware with a tempered software or firmware that displaysor forwards manipulated measurement data, e.g., data representingconsumption lower than the real consumption. In this case a significanteconomic loss could be the consequence for the utility company.

To prevent the software stored in the control unit 20 from beingtampered with or to detect a tampered software stored in the controlunit 20, the power meter 10 includes a security unit 14 which isconfigured to validate that a software or firmware stored in the memory22 of the programmable control unit 20 is authorized. The security unit14 can be implemented as a hardware security module (HSM). According toone embodiment, the metrology unit 11 and the security unit 14 areimplemented in a common module or housing (illustrated in dashed linesin FIG. 1). This module or housing 10 may include additional securitymeans (not shown) like security switches which, for example, may disablethe power meter in case the module or housing 10 is opened or is triedto be opened, or which alert the utility company.

The security unit 14 is coupled to the control unit 20 via acommunication link. This communication link can be a dedicatedcommunication link as illustrated in FIG. 1. According to a furtherembodiment, which is illustrated in FIG. 2, the power meter 10 includesa communication bus 18 to which the control unit 20, the metrology unit11 and the security unit 14 are coupled and which allows a communicationbetween these units.

Methods for software authentication are commonly known. Any of theseconventional methods can be performed by the security unit 14 in orderto verify that the software stored in the memory 22 is authenticated orauthorized. One embodiment of a software authentication method, whichmay be implemented by the security unit 14 and the control unit 20, isschematically illustrated in FIG. 3. In this method, the memory 22 ofthe control unit 20 includes two memory sections: A first section 22 ₁in which a program code is stored; and a second section 22 ₂ in which anauthentication information is stored. The authentication information is,for example, an encrypted version of a checksum of the program code orof parts of the program code stored in the first section 22 ₁. Thechecksum is, for example, obtained from the program code using securehash algorithms (SHA), like SHA1 or SHA256. Secure hash algorithms areone way functions, so that based on the checksum the program code cannotbe identified. The checksum stored in the second section 22 ₂ is furtherencrypted using a first one of a pair of keys. A second one of this pairof keys is stored in the security unit 14 and allows the security unit14 to decrypt the authentication information in order to retrieve thechecksum. The first key is, a secret key only known to the utility andused to decrypt the checksum, whereas the second key is a public key.This second key can be stored in the security unit 14 or the controlunit 20. The security unit 14 further applies the secure hash algorithmto the program code stored in the first section 22 ₁ and compares theresult of applying the hash algorithm to the program code with thechecksum obtained by decrypting the authentication information. If thechecksum equals the result of applying the hash algorithm, thesoftware/firmware stored in the memory 22 is considered to beauthorized. Again, the method illustrated in FIG. 3 is only one of aplurality of different methods for performing software authentication.Each of these other methods may be implemented in connection with thepower meters illustrated in FIGS. 1 and 2 instead of the methodillustrated in FIG. 3. If the result of the authentication process wouldbe that the software stored in the memory is not authorized, it isdiscarded/deactivated according to one embodiment.

Referring to FIG. 4, the power meter 10 according to a furtherembodiment includes a switching circuit 16, also known as circuitbreaker. The switching circuit 16 includes a switching element with aload path which is configured to be connected to the power line 100 or,more precisely, which is configured to be connected between twoterminals of the power line 100. The switching circuit 16 receives acontrol or drive signal S16 at a control input and is configured toassume and latch an on-state or an off-state each time it is driven. Inthe on-state the switching circuit 16 allows a current to flow throughthe power line 100, while in the off-state the switching circuit 16prevents a current to flow, i.e., interrupts the power line 100. Theswitching circuit 16 may include a conventional switching element, likea relay or a semiconductor power switch, and a drive circuit for drivingthe switching element dependent on the control or drive signal S16. Suchswitching circuits or circuit breakers are commonly known so that nofurther explanations are required in this regard.

In FIG. 1, only one power line is illustrated. Consequently, only oneswitching element of the switching circuit 16 is schematicallyillustrated in FIG. 4. Of course, the power meter can be connected tomore than one power line, like three power lines in a three-phase powersystem. In this case, the switching circuit includes a number ofswitches corresponding to the number of power lines, wherein each ofthese switches is connected to one of the power lines. These severalswitches of the switching circuit can be controlled or driven commonlyby the controller drive signal S16.

In the embodiment illustrated in FIG. 4, the drive signal S16 isprovided by the security unit 14. In this embodiment, the switchingcircuit 16 is directly connected to the security unit 14. However, thisis only an example. The security unit 14, and/or switching circuit 16could also be connected to the signal bus 18 and could receive the drivesignal S16 from the security unit 14 via the signal bus 18.

The security unit 14 might be, for example, configured to switch off theswitching circuit 16 when it detects that a non-authorized software isstored in the control unit 20, i.e. after the software authenticationprocess has failed.

FIG. 5 illustrates a further embodiment of a power meter 10. In thisembodiment, the control unit 20 includes a first interface circuit 25which is configured to connect the control unit 20 to a network 31. Thefirst interface circuit 25 enables a data communication between thecontrol circuit 20 and the electricity or utility company 41. Thenetwork 31 can be a conventional data communication network, like atelephone network, a wireless network, or a power line network adaptedfor power line communication.

A data communication between the control circuit 20 and the electricitycompany 41 can include: the transmission of power consumption data fromthe control unit 20 to the utility company 41 via the network 31; thetransmission of software updates for the software stored in the memory22 and running on the control unit 20; the transmission of controlinformation (for the switching circuit 16, for example) or of controldata (like tariff data, for example) from the utility company 41 via thenetwork 31 to the control circuit 20. By means of the controlinformation the utility company 41 may remotely actuate, i.e., switch onor off, the circuit breaker 16. Power consumption retrieved by thecontrol unit 20 from the metrology unit 11 and transmitted via thenetwork 31 to the utility company 41, allow the electricity company tobill the customer based on his energy consumption, wherein an on-sitereading of the power consumption or energy consumption data is notrequired.

Via the network 31 the utility company 41 can verify that the powermeter 10 which communicates or which tries to communicate with theutility company 41 is a power meter authorized by the utility company 41or by another trusted entity. An embodiment of a method for verifyingwhether the power meter 10 is an authorized power meter is schematicallyillustrated in FIG. 6. In this embodiment, the utility company 41 holdsa public key selected from a pair of keys with a public key and aprivate key, and the security unit 14 of the power meter holds thecorresponding private key 15. This pair of keys with can be generated ina conventional way and can be provided to the utility company 41 and thesecurity unit 14 in a conventional manner. These keys can be constant orthese keys can be session keys which are negotiated securely at thebeginning of the session. In order to verify the authorization of thepower meter, the utility company 41 sends a challenge to the securityunit 14 via the network 31 and the control unit 20. The security unit 14encrypts the challenge with the private key stored in the security unit14 and forwards the encrypted challenge to the utility company 41. Theutility company 41 decrypts the encrypted challenge using the public keystored in the utility company 41 and compares the decrypted responsereceived from the security unit 14 with the challenge originallyforwarded to the security unit 14. If the challenge originally forwardedto the security unit 14 corresponds to the decrypted response, thepublic key stored in the utility company 41 and the private key storedin the security unit 14 are corresponding keys. In this case, the powermeter is considered to be an authorized power meter.

In an equivalent manner, the power meter, in particular the securityunit 14 implemented in the power meter, can verify that the entityrequesting consumption data from the power meter via the network 31 orforwarding control data to the power meter, like data for switching onor off the circuit breaker 16, is an authorized entity. An embodiment ofa method enabling the security unit 14 to verify that the entityrequesting data or forwarding control data, like the utility company 41,is an authorized entity, is illustrated in FIG. 7. In this method, thesecurity unit 14 holds a public key and the utility model 41 holds thecorresponding private key. For verification purposes, the security unit14 via the control unit 20 and the network 31 forwards a challenge tothe utility company 41. The utility company 41 encrypts the challengeusing the private key and forwards a response to the security unit 14,wherein the response is the encrypted challenge. The security unit 14decrypts the response received from the utility company 41 using thepublic key and compares the result of the decryption process with thechallenge originally forwarded to the utility company 41. If thechallenge corresponds to the decrypted response, the utility company 41is considered to be authorized.

According to one embodiment, the power meter arrangements transmitspower consumption data to the utility company 41 only after it hassuccessfully been verified that the utility company 41 is authorized,using, for example, the method illustrated in FIG. 7. Further, the powermeter is configured to accept requests from the utility company 41 totransmit power consumption data or to accept control data received fromthe utility company 41 only after it has been successfully verified thatthe utility company 41 is authorized, using, for example, the methodillustrated in FIG. 6.

Additionally or alternatively to authenticating the power meter and theutility company 41, the communication between the utility company 41 andthe power meter can be encrypted. This communication may include powerconsumption data transmitted from the power meter to the utility company41, or may include data requests or control data transmitted from theutility company 41 to the power meter. Encrypting the communicationbetween the power meter and the utility company 41 may include the useof a key pair with a public key and a private key, wherein one of thepower meter and the utility company 41 encrypts the information to betransmitted using a public key, and the other one of the power meter andthe utility model 41 decrypts the encrypted information using thecorresponding private key. In the power meter, the key involved in thiskind of communication can be stored in the security unit 14, which canbe implemented as a hardware security module.

In the power meter, the encryption of data transmitted to the utilitycompany 41 or the decryption of data or control information receivedfrom the utility company 41 is performed by the security unit 14. Forthis, the security unit 14 receives the data to be transmitted to theutility company 41, like data from the metrology unit 11, and encryptsthese data before transmitting the data to the utility company 41 viathe control unit 20 and the network. Likewise, the security unit 14receives data or information transmitted by the control unit 20,decrypts these data or information and forwards the decryptedinformation to the respective units in the power meter, like the circuitbreaker 16 or the metrology unit 11. Data received from the utilitycompany 41 for the metrology unit 11 can be data which resets themetrology unit, for example, after the power consumption data have beenread from the metrology unit 11 and forwarded to the utility company 41.Data or information received by the circuit breaker 16 are switchinginformation which switch on or off the circuit breaker 16.

According to a further embodiment, the encryption and decryption of datato be transmitted or received, respectively, is not performed by thesecurity unit 14, but is performed by the control unit 20. In this case,the security unit 14 (which can be implemented as a hardware securityunit) stores the encryption/decryption keys required for theencryption/decryption process and provides these keys to the controlunit 20.

The function of the security unit 14 is to provide a secure datacommunication between the power meter arrangement and the electricitycompany. “Secure data communication” in this connection means that dataprovided by the power meter arrangement, like power consumption data,are only disclosed to an authorized entity at the electricity company41, and that external data, like control data for the circuit breaker 16or software updates for the logic unit 21 are only accepted from theauthorized entity at the electricity company. Further, the hardwaresecurity unit securely stores all the keys required in the power meterarrangement, like keys for communication and keys required for verifyingthe authentication of the software stored in the control unit 20.According to a further embodiment, the security unit 14 is configured tosecurely store measurement data or a history of measurement dataprovided by the metrology unit 11 (which can then be transmitted toutility company). According to yet another embodiment, the security unit14 is also configured to store information on tampering attempts. Suchtampering attempts may include the storing of non-authorized software inthe control unit 20, wherein this type of tampering attempt can bedetected using the method explained in detail hereinbefore. According toone embodiment, the metrology unit 11 is configured to receive tariffinformation. This tariff information can be used in the evaluation unit13 to calculate the energy price based on the power consumption.

According to one embodiment, tariff information stored in the evaluationunit 13 can be provided to electrical loads via the logic unit 21 and afurther network 32, like a home area network (HAN). These loads arefurther connected to the power line for power supply purposes. Thistariff information in the electrical loads can, for example, be used toprevent the operation of electrical loads when, for example, the tariffis not a given tariff.

Referring to FIG. 5, the power meter arrangement may additionallyinclude a power down control of a voltage supply circuit 17 connected tothe power line 100 and configured to provide a supply voltage for thecircuitry of the power meter arrangement. In order to avoid anunauthorized disabling of the power meter 10 by sending it to sleep modethrough a command issued by the control unit 20, this function may alsobe managed through the security unit 14.

Besides the authentication and encryption/decryption functionality, thesecurity unit 14 may store all secret keys for the different encryptionpurposes used in the system, like secret keys for authentication orencryption/decryption purposes; verify the integrity of the power meterby verifying certain behavior; or generate and evaluate certificates, toupdate secret keys or to implement additional security functions.

Although various exemplary embodiments of the invention have beendisclosed, it will be apparent to those skilled in the art that variouschanges and modifications can be made which will achieve some of theadvantages of the invention without departing from the spirit and scopeof the invention. It will be obvious to those reasonably skilled in theart that other components performing the same functions may be suitablysubstituted. It should be mentioned that features explained withreference to a specific figure may be combined with features of otherfigures, even in those cases in which this has not explicitly beenmentioned. Further, the methods of the invention may be achieved ineither all software implementations, using the appropriate processorinstructions, or in hybrid implementations that utilize a combination ofhardware logic and software logic to achieve the same results. Suchmodifications to the inventive concept are intended to be covered by theappended claims.

What is claimed is:
 1. An electric power meter arrangement, comprising: a metrology unit that is configured to be coupled to a power line, to determine a power consumption, and to provide measurement data representing the power consumption; a programmable control unit including a memory that stores software configured to run on the control unit; a security unit coupled to the control unit by a communications link, the security unit configured to store at least one key and to determine whether the software stored in the memory of the programmable control unit has been altered without authorization; and a switching circuit comprising at least one switching element configured to be connected to the power line and configured to be switched on or off dependent on a drive signal received by the switching circuit, wherein the security unit is configured to receive drive information for the switching circuit from the control unit, to check a validity of the drive information, and to generate the drive signal dependent on the drive information only if the drive information has been determined to be valid.
 2. The electric power meter arrangement of claim 1, wherein the at least one key comprises a secret key.
 3. The electric power meter arrangement of claim 1, wherein the at least one key comprises a public key.
 4. The power meter arrangement of claim 1, wherein the control unit further comprises: at least one first interface circuit which is configured to connect the control unit to a network.
 5. The power meter arrangement of claim 1, further comprising a display coupled to the control unit.
 6. The power meter arrangement of claim 1, wherein the control unit is configured to store measurement data.
 7. The power meter arrangement of claim 6, wherein the security unit is configured to read out stored measurement data upon receipt of a request from the control unit, and wherein the security unit is configured to check a validity of the request, and to read out the measurement data only if the request has been determined to be valid.
 8. The power meter arrangement of claim 1, wherein the security unit is further configured to store measurement data.
 9. The power meter arrangement of claim 1, wherein the security unit is further configured to verify an integrity of the power meter arrangement by verifying certain behavior.
 10. The power meter arrangement of claim 1, wherein the security unit is further configured to generate or evaluate certificates.
 11. The power meter arrangement of claim 1, wherein at least one of the control unit and the security unit is configured to store at least one of tariff information, date information, and/or time information.
 12. A method of monitoring power, the method comprising: determining a power consumption of a power line by a metrology unit; operating a control unit using software stored in memory of the control unit; receiving data from the metrology unit by the control unit; transmitting a key stored in a security unit to the control unit; determining whether the software stored in the memory of the control unit has been tampered with using the key; transmitting drive information for a switching circuit from the control unit to the security unit; checking a validity of the drive information; and generating a drive signal based on the drive information when the drive information is valid.
 13. The method of claim 12, wherein determining whether the software stored in the memory of the control unit has been tampered with comprises: retrieving an encrypted version of a checksum of the software stored in the memory of the control unit; decrypting the checksum using a private key; retrieving a public key; applying a hash algorithm to the software stored in the memory of the control unit; comparing a result of the hash algorithm to the checksum; and deactivating the software if the result of the hash algorithm is unequal to the checksum.
 14. The method of claim 12, further comprising preventing power from being transmitted by the power line when the software stored in the memory of the control unit has been tampered with.
 15. The method of claim 12, further comprising: transmitting data from the control unit to a utility company using a network; transmitting software from the utility company to the control unit using the network; and transmitting control information or control data from the utility company to the control unit.
 16. The method of claim 12, further comprising powering down a voltage supply circuit connected to the power line when software stored in the memory of the control unit has been tampered with.
 17. A system for monitoring a power line, the system comprising: a metrology unit configured to be coupled to the power line, the metrology unit comprising a sensing device configured to be coupled to the power line, and an evaluation unit configured to calculate a power consumption based on an output of the sensing device and determine measurement data based on the power consumption; a control unit configured to receive measurement data from the metrology unit and to transmit data to the metrology unit, the control unit comprising memory, the memory configured to store a software program, and a first interface circuit configured to connect the control unit to a network; a security unit coupled to the control unit, the security unit configured to detect whether the software stored in the memory of the control unit has been tampered with, and transmit a key stored in a security unit to the control unit; and a switching circuit configured to be connected between two terminals of the power line, wherein the switching circuit coupled to the security unit, the switching circuit comprises at least one switching element configured to be connected to the power line and configured to be switched on or off dependent on a drive signal received by the switching circuit, and the security unit is configured to receive drive information for the switching circuit from the control unit, to check a validity of the drive information, and to generate the drive signal dependent on the drive information only if the drive information has been determined to be valid. 